#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;

int main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    
    int n;
    cin >> n;
    
    vector<int> a(n);
    rep(i, n) cin >> a[i];

    const int MAXA = 200000;
    const int MAX_SUM = 2*MAXA; 
    const int B = 500;            
    const int LIM = MAX_SUM/B;

    ll ans = 0;
    for (int m = 1; m <= B; ++m) {
        map<int,int> cnt;
        rep(j, n) cnt[a[j]-m*(j+1)]++;
        rep(i, n) {
            auto it = cnt.find(a[i]-m*(i+1));
            if (it != cnt.end()) {
                if (--(it->second) == 0) cnt.erase(it);
            }
            auto it2 = cnt.find(m*(i+1)-a[i]);
            if (it2 != cnt.end()) ans += it2->second;
        }
    }

    rep(i, n) {
        int maxj = min(n, LIM-i);
        if (maxj <= i) continue;
        for (int j = i+1; j <= maxj; ++j) {
            int s = i+j+2;
            int sum = a[i]+a[j];
            if (sum%s == 0) {
                if (sum/s > B) ++ans;
            }
        }
    }

    cout << ans << "\n";
    
    return 0;
}